The goal is to develop instrumentation and procedures for bronchoscopically localizing carcinoma in situ and very small areas of mucosal carcinoma in individuals with positive sputum cytology and negative chest X-ray, not possible by routine fiberoptic bronchoscopy. The imaging fluorescence bronchoscopy employs violet light (410 nm) from a laser and an image intensifier and is carried out 72 hours after a single intravenous injection of hematoporphyrin derivative (2 to 2.5 mg/kg). The potential of this method has been realized in that in two patients, small areas of CIS were localized solely by their fluorescence, which areas visibly (white light) showed normal appearing mucosa. This method is very supersensitive (over 90%). Research is now directed at real-time digital computer analysis to sharpen edges of very small fluorescing areas and to enhance contrast with backgrounds.